In my copending application, Ser. No. 593,985, filed July 8, 1975, there is disclosed an improved locking type spark plug gasket and tool for installing the same in which a plurality of S-folded sealing flanges terminate in an angularly disposed segmented locking flange which extends radially inwardly of the sealing flanges at an angle thereto. During installation, a hollow cylindrical tool surrounds the threaded shank in such manner that the free circular edge thereof contacts surfaces of the locking flange to deform the same to a plane parallel to that of the sealing flanges, in which condition the segmented edge of the locking flange is positioned within a circular undercut recess between a radial surface of the spark plug body and the inner end of the threaded portion of the shank. At the completion of installation, very little distortion of the inner end of the locking flange occurs, owing to the segmented configuration thereof.
Certain brands of spark plugs manufactured in the United States and elsewhere are provided with spark plug bodies, the shanks of which are threaded by a rolling operation rather than by cutting, and in which the thread extends at its inner end to the radially positioned surface of the plug body from which the shank extends, without any circular recess whatsoever. In such construction, gaskets of the type disclosed in the above mentioned application cannot be uniformly staked in position owing to the absence of the recess, and in the case of rolled threads, there is a tendency to accumulate varying degrees of excess metal at the inner end of the above thread, such that prior art gaskets designed for this type of threaded shank do not engage the shank properly. In a hand staking operation this presents less difficulty. In commercial manufacture, however, it is usual to install the gasket as a completely automated line of operation, and the inability of a gasket to properly seat gives rise to malfunctioning a machinery making the installation, and an improperly seated gasket will not properly seal when the plug is installed in an engine.